It is known practice from the publication of Pfaff Industriemaschinen GmbH entitled "PFAFF 200-04 Special Service" to sew together the associated strip of cloth on a left trouser forepart, the so-called left fly lining, and the associated area of the trouser forepart. The sewn-on strip of cloth is then folded over and the associated zip-fastener half, i.e. the left zip-fastener component, is sewn on. This strip of cloth is subsequently folded over again and the left joining seam is produced between the strip of cloth and the trouser forepart. Also, the sewing of the right strip of cloth having the right zip-fastener component, i.e. the associated zip-fastener half, on to the right trouser forepart takes place in several work cycles.
It is known practice from U.S. Pat. No. 4,534,067 to manufacture trouser flies in such a manner that an additional strip of cloth is also cut in one piece with each of the two trouser foreparts in the fly area and is then folded over and sewn together with the trouser forepart. In addition, a zip-fastener half, i.e. a zip-fastener component, is also sewn on. In the case of the left trouser forepart the outer edge is pressed inwards so that a four-layered design is formed in this case which is then stitched.